Bang after water is turned off

[workhorse]

Hope someone can help here.
Recently when we flush a toilet or turn off the cold taps as the water cuts off there is a bang sound which is quite sharp and sounds of impending heavy costs, we have a mega-flow system if that is important
Thanks

Workhorse

 

[keego]

Check your stop tap & make sure it's fully open.

 

[possum_jenkins]

Will be a washer in the fov in a toilet.

 

[workhorse]

Thanks for reply, but what sort of washer in a toilet?